Division head curtain for compartmented grinding mill

ABSTRACT

A grinding mill is disclosed having a cylindrical shell for rotation about its central axis, and a division head that divides the interior of the shell into axially disposed compartments, one compartment containing steel rods for relatively coarse grinding and another compartment containing steel balls for finer grinding. A passage defining liner extends through the division head assembly and defines a central passage through the division head assembly with a surface having the configuration of a truncated cone with its central axis coincident with the central axis of the shell and with its apex end pointed toward the coarse grinding compartment. A shielding disk is concentrically mounted within the conical central passage in a plane perpendicular to the shell axis and supported by a plurality of arcuately spaced mounting blocks between the outer periphery of the shielding disk and the inner periphery of the conical central passage. Channels are defined between the disk, a pair of adjacent blocks, and the inner surface of the surrounding liner. A plurality of curtain strips are attached to the disk and arranged to extend radially outward to cover each channel. The strips have greater radial length than the distance between the disk and the liner, and the end of each strip is turned away from the rod compartment end of the liner. The strips thereby block grinding balls from migrating through the channels into the rod compartment, but the ends of the strips pivot away from the rod compartment end of the liner as pulp flows from the rod compartment through the liner and into the ball compartment of the mill.

United States Patent 1191 Olson et al.

[ 51 Sept. 11, 1973 [75] Inventors:' Donald R. Olson; Eugene P. Waddell,

both of Brookfield, Wis.

[73] Assignee: Allis-Chalmers Corporation,

Milwaukee, Wis.

{221 Filed: May 15, 1972 [21] Appl. No.: 253,534

152] US. Cl. 241/153, 241/171 Primary Examiner-James L. Jones, Jr. Assistant Examiner-E. F. Desmond. Aztorney Arthur M. Streich et al;

[57] ABSTRACT A grinding mill is disclosed having a cylindrical shell for rotation about its central axis, and a division head that divides the interior of the shell into axially disposed compartments, one compartment containing steel rods for relatively coarse grinding and another compartment containing steel balls for finer grinding. A passage defining liner extends through the division head assembly and defines a central passage through the division head assembly with a surface having the configuration of a truncated cone with its central axis coincident with the central axis of the shell and with its apex end pointed toward the coarse grinding compartment. A shielding disk is concentrically mounted within the conical central passage in a plane perpendicular to the shell axis and supported by a plurality of arcuately spaced mounting blocks between the outer periphery of the shielding disk and the inner periphery of the conical central passage. Channels are defined between the disk, a pair of adjacent blocks, and the inner surface of the surrounding liner. A plurality of curtain strips are attached to the disk and arranged to extend radially outward to cover each channel. The strips have greater radial length than the distance between the disk and the liner, and the end of each strip is turned away from the rod compartment end of the liner. The strips thereby block grinding balls from migrating through the channels into the rod compartment, but the ends of the strips pivot away from the rod compartment end of the liner as pulp flows from the rod compartment through the liner and into the ball compartment of the mill.

4 Claims, SDrawing Figures DllVlSlON HEAD CURTAIN FOR COMPARTMENTED GRINDING MILL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to multiple compartment cylindrical grinding mills having a compartment containing steel rods for coarse grinding, a compartment containing steel balls for finer grinding, and a division head assembly between the compartments. In particular this invention is an improvement to the mill disclosed in U.S. Pat. No. 3,624,797.

2. Description of the Prior Art In addition to the aforementioned U.S. Pat. 3,624,797, grinding mills having a cylindrical shell divided into longitudinally disposed compartments by a division head assembly, are also shown in prior art patents such as U.S. Pat. Nos. 2,052,426 of 1936; 3,144,212 of 1964; 3,298,619 of 1967; 3,601,323 of 1971 and German Pat. 467,522. The aforementioned U.S. Pat. No. 2,052,426 also discloses a division head assembly having a pair of spaced annular bulkheads, and a conical liner connected on its apex and to the central opening in each of the annular bulkheads of the division head assembly. In this prior art patent the conical liner connected to the coarse side bulkhead does not extend to the fine side bulkhead. Such an arrangement provides for pulp in both compartments to flow into a central discharge chamber rather than a one direction through-flow movement of pulp from the coarse grinding compartment, through the division head assembly, to the fine grinding compartment. With the central discharge mill, rather than a one direction end to end movement of pulp, much greater classifier capacity must be provided because partly ground material which needs further grinding and finely ground material needing no further grinding, are mixed and discharged together through a common discharge port in a central portion of the mill.

For a one direction through-flow movement of pulp requiring less classifier capacity, the prior art discloses division head assemblies and mill arrangements such as are disclosed in U.S. Pat. Nos. 3,144,212 and 3,298,619. However, in actual practice utilizing such mills with such division head assemblies, which include a slotted bulkhead on the fine grinding side of the division head, pieces of the steel grinding balls are forced through the slotted bulkhead and into the coarse grinding compartment containing steel grinding rods. Such pieces in the rod compartment get between the rods and hold the rods apart, not allowing them to come sufficiently close together to break pulp material and these prior art constructions therefore, like the central discharge mills, also have disadvantages.

ln U.S. Pat. No. 3,601,323 a grinding mill is also disclosed having a cylindrical shell for rotation about its central axis and a division head that divides the interior of the shell into axially disposed compartments, one

compartment containing steel rods for relatively coarsewith a surface having a configuration of a truncated cone with its central axis coincident with the central axis of the shell, and with the apex end of the configuration pointed toward the coarse grinding compartment.

Such a conical configuration of the central opening through the division head from the rod compartment to the ball compartment eliminates the need for slotted openings in one of the bulkheads and provides a downwardly sloped path from the coarse grinding chamber 'to the fine grinding chamber. During normal operation of the mill the slope of the path inhibits balls moving through the division head from the ball compartment into the rod compartment because during normal operation the grinding balls will find it difficult to roll up the slope. Balls that enter the rod compartment via a path external to the shell, as in a closed grinding circuit, can

- roll down the slope from the rod compartment back into the ball compartment. However, while such a division head does provide the described result in normal operation, during periods of mill acceleration at startup and during periods of deceleration when the mill is stopping, the charge of grinding balls in the fine grinding compartment tends to surge toward the division head. During such periods the grinding balls could move much more easily up the slope of the central passage through the division head and then to the rod compartment where they interfere with the grinding action of the rods. It was to this problem that U.S. PateNo. 3,624,797 was directed and according to that patent a shielding disk is concentrically mounted within the conical central passage through the division head as- SUMMARY OF THE PRESENT INVENTION Despite the advances in this technology provided by the aforementioned patents, a problem has persisted with mills disclosed in U.S. Pat. No. 3,624,797 in that balls have migrated through the pulp flow channels from the ball compartment into the rod compartment, counter to the flow of pulp therethrough from the rod compartment to the ball compartment. It is an object of this invention to prevent such migration of balls into the rod grinding compartment where the presence of such balls can prevent rods coming together in parallel or near parallel alignment for best grinding action.

In a preferred embodiment of the present invention a shielding disk and pulp flow channels are provided as disclosed in U.S. Pat. No. 3,624,797 and additionally a plurality of curtain strips are attached to the disk and arranged to. extend radially outward to cover each channel. The strips have greater radial length than the distance between the disk and the liner and the end of each strip is turned away from the rod compartment end of the liner. The strips thereby block grinding balls from migrating through the channels into the rod compartment but the ends of the strips pivot away from the rod compartment end of the liner as pulp flows from the rod compartment through the channels into the ball compartment of the mill.

Other features and objects of the invention that have been attained will appear from the more detailed description to follow with reference to an embodiment of the present invention shown in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the accompanying drawing shows a side elevation, in section, of a grinding mill according to the present invention;

FIG. 2 shows to enlarged scale an end view of the central portion of the division head assembly shown in FIG. 1, view from the discharge end of the mill; and,

FIG. 3 is a view of a portion of the division head assembly shown in FIG. 2, taken along lines A, B, C in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The multi-stage grinding mill disclosed in FIG. 1 of the drawing comprises a rotary cylindrical shell casing 1 illustrated as having uniform or substantially uniform diameter throughout its length, with the casing being provided with feed and discharged end heads 2, 3, respectively. The casing 1 is divided into a pair of grinding chambers 4 and 5 in a manner and by a structure that will be described in detail later. The chamber 4 on the inlet end of the casing l is provided with a plurality of rods 6 that provide for relatively coarse grinding in the chamber 4. The chamber 5 is provided with a plurality of balls 7 for relatively fine grinding of material in chamber 5. The mill is rotatably mounted and suitable end bearings carry feed and discharge trunnions l1 and 12, respectively. Rotary motion about its horizontal central axis may be imparted to the mill by means of power applied to a driving gear 13 secured around the casing l. The feed end of the mill is provided with a feeder 15 for introducing the material which is to be reduced, into the inlet end of the coarse grinding chamber 4 through the feed trunnion 11.

The discharge end of chamber 5 is provided with a perforated plate 19 which is spaced from the end head 3. Located within the space between the plate 9 and the end head 3 is a series of elevating vanes 20. The inner extremities of the elevating vanes 20 are located close to a central discharge cone 2], the apex of which is directed toward the discharge trunnion 12.

The arrangement shown in FIG. 1 for dividing the casing 1 into the two grinding compartments 4 and 5, includes an arrangement of parts shown to enlarged scale in FIGS. 2 and 3. A division head assembly is mounted within the mill comprising a pair of spaced annular bulkheads 26, 27. The side of bulkhead 26 facing the feed head 2 and the side of bulkhead 27 facing the discharge head 3, are each provided with replaceable wear liners 28, 29, respectively. Liner 29 projects farther radially inwardly than does bulkhead 27 but the reverse is true on the opposite side of the division head assembly where the liner 28 does not project as far radially as bulkhead 26'thus leaving an inner portion of bulkhead 26 unprotected by liner 28. The inner portion of bulkhead 26 not protected by liner 28 is however covered and protected by a liner 30 having both a radial portion 31 and an axially extending portion 32. A liner extends between the axial extending portion 32 of liner 30 and the radially inner portion of liner 29, and portion 32 and liner 35 together provide and define a central passage 36 through the division head assembly 25 having openings 37, 38 and a configuration therebetween of a truncated cone with its apex end pointed toward the feed head end 2 of the mill and a base flange 39 on the end thereof facing the discharge end 3.

Shielding means comprising a disk 40 is mounted concentrically within the central passage 36 and perpendicular to the central axis X-X. A plurality of mounting blocks 41 are connected to the outer periphery of disk 40, as by welding, and blocks 41 are connected to the inner periphery of liner 35 by bolts 42 that pass through the blocks 41, liner 35, bulk head 26 and liner 30 to unite assembly of those parts. A peripheral pulp channel 43 is defined between each adjacent pair of blocks 41 and the outer circumference of the disk 40.

Curtain means, comprising a plurality of curtain strips 50 are attached to the disk 40 by bolts 51 and nuts 52 (See FIG. 3). The strips 50 may be made of any suitable material such as rubber, reinforced rubber, woven wire matting, carpeting or the like. As shown in FIG. 2, the strips 50 extend radially outward from the disk 40 to cover each channel 43. As shown in FIG. 3, the strips 50 have greater radial length than the distance between disk 40and liner 35, and an end portion 53 of each strip 50 is turned away from the rod compartment end of the liner 35.

In the operation of the mill assembly that has been described, material to be ground is delivered to the feeder 15 and fed into the coarse grinding chamber 4 where the rods, which tumble as gear 13 turns casing 1, provide a preliminary grinding of the feed material to provide a coarse pulp which will flow from chamber 4 through the passage 36 in the division head assembly 25 and into chamber 5. In chamber 5 the steel balls 7 tumble and provide a further grinding action to provide a finer pulp which flows through the perforated plate 19 to be picked up by the vanes 20 and dumped into the discharge cone 21. With the central passage 36 through division head assembly 25 being defined by liner 35 and a portion 32 of liner 30, which in turn provide a configuration of a truncated cone with its central axis coincident with the central axis of the known shell 1 and with the apex end of this configuration pointed toward the chamber 4, the bottom surface of this passage 36 is sloped downwardly from the rod chamber toward the ball chamber 5.

During periods when the mill is being started and being accelerated to operating speed and when the mill is being slowed in preparation for shutdown, surges of masses of grinding balls 7 toward the division head assembly 25 are restrained from passing through the passage 36 to the rod compartment 4, by the shielding disk 40 and during such periods as well as during normal operation, individual balls are blocked from migrating through the channels 43 into the rod compartment 4 by the strips 50. A ball 7 moving toward a strip 50 as shown in FIG. 3, tends to wedge'the end portion 53 of strip 50 against the converging sloped inner surface of liner 35 and effectively prevent the ball 7 passing therethrough. During normal operation of the mill when the mill is being rotated at steady and constant rate, pulp flows freely from the rod compartment 4, through the channels 43 and into the ball compartment 5 with the flexible strips 50 pivoting away from the converging end of liner 35 to open channels 43 for free flow therethrough, while at the same time a strip 50 would block a ball 7, as shown in FIG. 3, from bouncing through an upper portion of passage 36.

From the foregoing detailed description of the present invention, it has been shown how the objects of.the invention have been obtained in a preferred manner. However, modification and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to be included within the scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. [n a grinding mill having a cylindrical shell mounted for rotation about its central axis, a compartment containing media for coarse grinding and a compartment containing media for finer grinding separated by a division head assembly, a passage defining liner extending through the division head assembly and the liner having an inner surface defining a central passage through the division head assembly with its surface having a configuration of a truncated cone with a central axis coincident with the central axis of the shell and with an apex end pointed toward the coarse grinding compartment, and shielding means within said central passage presenting a surface blocking a central portion of the passage and defining peripheral channels'therethrough and improvement comprising i (a) Flexible curtain means projecting radially outward from the shielding means to cover each of the peripheral channels;

(b) The curtain means being attached to the shielding means and extending radially outward into engagement with the inner surface of the liner to block fine grinding media from migrating through the channels toward the apex end of the liner and into the coarse grinding compartment; and,

(c) The radial outer ends of the curtains being pivotal about the shielding means in a direction away from the apex end of the liner to provide open pulp channels therethrough from the coarse grinding compartment to the fine grinding compartment.

2. A grinding mill according to claim 1 characterized in that the curtain means covering each said peripheral channel comprises a plurality of radially extending strips of flexible material.

3. A grinding mill according to claim 2 characterized in that the shielding means comprise a disk concentrically mountedwithin said central passage and perpendicular to said central axis, and a plurality ofj mounting blocks connecting the disk to the liner and supporting the disk to block a central portion of the central passage and provide a pulp channel between the outer periphery of the disk and the inner periphery of the liner with said strips projecting radially outward from said disk and between adjacent of said blocks. i Y

4. The structure of claim 3 characterized in that the strips have a greater radial length than the radial distance between the disk and the liner, with the end of each strip turned away from the apex end of the liner. 

1. In a grinding mill having a cylindrical shell mounted for rotation about its central axis, a compartment containing media for coarse grinding and a compartment containing media for finer grinding separated by a division head assembly, a passage defining liner extending through the division head assembly and the liner having an inner surface defining a central passage through the division head assembly with its surface having a configuration of a truncated cone with a central axis coincident with the central axis of the shell and with an apex end pointed toward the coarse grinding compartment, and shielding means within said central passage presenting a surface blocking a central portion of the passage and defining peripheral channels therethrough and improvement comprising: (a) Flexible curtain means projecting radially outward from the shielding means to cover each of the peripheral channels; (b) The curtain means being attached to the shielding means and extending radially outward into engagement with the inner surface of the liner to block fine grinding media from migrating through the channels toward the apex end of the liner and into the coarse grinding compartment; and, (c) The radial outer ends of the curtains being pivotal about the shielding means in a direction away from the apex end of the liner to provide open pulp channels therethrough from the coarse grinding compartment to the fine grinding compartment.
 2. A grinding mill according to claim 1 characterized in that the curtain means covering each said peripheral channel comprises a plurality of radially extending strips of flexible material.
 3. A grinding mill according to claim 2 characterized in that the shielding means comprise a disk concentrically mounted within said central passage and perpendicular to said central axis, and a plurality of mounting blocks connecting the disk to the liner and supporting the disk to block a central portion of the central passage and provide a pulp channel between the outer periphery of the disk and the inner periphery of the liner with said strips projecting radially outward from said disk and between adjacent of said blocks.
 4. The structure of claim 3 characterized in that the strips have a greater radial length than the radial distance between the disk and the liner, with the end of each strip turned away from the apex end of the liner. 